This invention relates to the melting, vaporization and spraying of materials and, more particularly, to such spraying induced by laser heating.
In many modern materials systems, it is necessary to add layers of a material to an existing substrate. In some circumstances, a coating of a hard, wear resistant material is overlaid onto a strong, ductile material. The resulting composite provides a structural component that has good mechanical properties such as strength, ductility, and fracture toughness, and also has a surface that does not wear rapidly in environments that are erosive and/or corrosive. In another application, a part can be repaired by adding to the substrate new material of the same composition as the substrate, gradually building up a thickness of the added material to replace that which may have been lost during service. Many other applications of coating are in widespread use, because of the versatility afforded in designing custom materials systems.
The layers of the material may be added to the substrate in many different ways, depending upon the substrate, the added material, and the performance required. The added material may be provided in a bulk form and laminated, bonded, or affixed to the substrate. Alternatively, the material to be added can be provided in a form different from its final configuration and applied to the substrate atomically, often in either the molten or vaporous state. In many instances, the latter type of approach is preferred to produce an excellent bond of the added material to the substrate and to produce a highly controllable final product.
In one widely practiced approach, a plasma is formed with an electric arc. Metal powder in a gas stream is directed through the plasma, causing the metal to melt, at least in part. The melted metal is then sprayed against a substrate to solidify as a coating or built-up layer. Plasma spraying and other similar techniques are not practical for some metals, such as, for example, titanium alloys sprayed in an atmospheric environment. When done in a vacuum, the technique becomes expensive.
Alternative techniques based upon the use of a laser as an energy source have been proposed. For example, U.S. Pat. Nos. 4,200,669 and 4,724,299 whose disclosures are incorporated by reference, have provided procedures and apparatus said to be effective in melting powdered materials and depositing them upon the substrate. Experience has shown, however, that these approaches are inefficient in depositing feed material at a high rate onto the substrate. However, the basic viability of the laser heating source has been established.
There therefore is a need for an apparatus which utilizes a laser heating source for the plasma deposition of a finely divided feed material, and achieves high deposition rates and efficiencies. Such an apparatus should be controllable and versatile. The present invention fulfills this need, and further provides related advantages.